Special coupled quantum Otto cycles

Selçuk Çakmak, Deniz Türkpençe, Ferdi Altintas

Ferdi Altintas

Selçuk Çakmak, Ferdi Altintas, Özgür Esat Müstecaplıoğlu

Małgorzata Bednarska, Andrzej Grudka, Paweł Kurzyński +2 more

Haena Shim, Joonhyun Yeo

We study finite-time quantum Otto cycles whose working medium is a harmonic oscillator undergoing a quantum Brownian motion described by the Caldeira-Leggett model when the oscillator is in contact with heat baths in isochoric processes. The time evolution of the Otto cycle is studied by analytically solving the exact Heisenberg-Langevin equations for the system variables and the interaction energy between the system and the bath. This enables us to investigate non-Markovian strong-coupling effects on the quantum Otto cycle. We obtain cyclic steady states and study the thermodynamic properties of the Otto cycle for various values of the parameters describing the heat baths and the coupling between the system and the bath. We compare our results with those obtained in the Markovian limit, where the time evolution is described by the Lindblad equation. We find that the change in the interaction energy during the isochoric process contributes to both work and heat and plays a crucial role in determining the thermodynamic behavior of the cycle. This is in contrast to the behavior of the state observables of the working medium, which show relatively small change compared to the Markovian counterparts. We find that non-Markovian effects only become significant when we consider thermodynamic fluxes such as work and heat with the system-bath interaction fully taken into account. We also compare our results with the power-efficiency trade-off relation recently proposed for the Markovian quantum Otto engine.

Zorar Ahmadi, B. Mojaveri

This study presents a comparative analysis of three quantum thermal engines utilizing a two-qubit Heisenberg XXZ chain as the working substance. A novel generalized quantum Otto cycle (GQOC) is introduced, featuring two distinct coupling configurations to thermal reservoirs. The GQOC exhibits the potential for 100% efficiency, surpassing the efficiency of the conventional quantum Otto cycle. Essential conditions for positive work extraction and achieving maximum unity efficiency are derived. An experimental implementation using quantum electrodynamic circuits and Transmon qudit is proposed. This work contributes to the advancement of quantum heat engines, highlighting the benefits of nonequilibrium processes and asymmetric coupling for enhanced work extraction and efficiency.